JOHNS HOPKINS (US) — The nervous system chemical that triggers a man’s erection also helps him maintain it, researchers say.

The discovery of the biochemical chain of events that keeps a male penis erect after the initial response may lead to new therapies to help men with erectile dysfunction.

“We’ve closed a gap in our knowledge,” says Arthur Burnett, professor of urology at the Johns Hopkins University School of Medicine. “We knew that the release of the chemical nitric oxide, a neurotransmitter that is produced in nerve tissue, triggers an erection by relaxing muscles that allow blood to fill the penis.

“We thought that was just the initial stimulus. In our research, we wanted to understand what happens next to enable that erection to be maintained.”

In a study of mice, Burnett and colleagues found a positive feedback loop in the penile nerves that triggers waves of nitric oxide to keep the penis erect. The key finding is that after the initial release of nitric oxide, a biochemical process called phosphorylation takes place to continue its release and sustain the erection.

In 1992, Burnett and Johns Hopkins colleague Solomon S. Snyder, a professor of neuroscience who is also a co-author of the new study, showed for the first time that nitric oxide is produced in penile tissue. That research demonstrated the key role of nitric oxide as a neurotransmitter responsible for triggering erections.

“Now, 20 years later, we know that nitric oxide is not just a blip here or there, but instead it initiates a cyclic system that continues to produce waves of the neurotransmitter from the penile nerves,” Burnett says.

Since the basic biology of erections in laboratory mice is the same as in humans, Burnett says, the new rodent research may open the way to new treatments for erection problems caused by diabetes, vascular disease, surgical nerve damage or other causes. Such new approaches could be used to intervene earlier in the arousal process than current medicines for erectile dysfunction.

“It has been a 20-year journey to complete our understanding of this process,” Snyder says. “Now it may be possible to develop therapies to enhance or facilitate the process.”

The National Institute of Diabetes and Digestive and Kidney Diseases funded the work. Other co-authors are at Johns Hopkins and at the University of Colorado and Morgan State University.